1. Field of the Invention
The invention relates to a sorting method, more particularly to a method for sorting a light source.
2. Description of the Related Art
In light source analysis, the CIE (Commission Internationale de l'éclairage) 1931 coordinates (referred to as CIE coordinates hereinafter) are generally adopted for defining a light color emitted from a light source. The CIE coordinates are usually represented in a form of (x, y), and each specific coordinate point (a, b) corresponds to a specific color. Moreover, a color which corresponds to a coordinate point (a, b) is similar to a color which corresponds to a coordinate point (a+Δx, b+Δy) proximate to the coordinate point (a, b). For example, pure white corresponds to a CIE coordinate point of (0.33, 0.33), so that a color which corresponds to a CIE coordinate point proximate to (0.33, 0.33) may be regarded as similar to pure white.
In addition, each specific light color corresponding to a specific CIE coordinate point (a, b) may be composed of different light components with respective wavelengths, that is, light sources which emit lights of different spectral compositions may emit a substantially same light color, and the light color corresponds to a substantially same CIE coordinate point. This characteristic is called metamerism of the CIE coordinate system. Therefore, in a condition that the CIE coordinates are adopted to analyze different light sources, when the light sources emit substantially the same light color which corresponds to substantially the same CIE coordinate point, the analyzed result may not be usable for determination as to whether the light sources have substantially the same spectral characteristic.
For instance, a white LED (light-emitting diode) package light source may be composed of a LED die in combination with appropriate fluorescent powder (for example, a blue LED die in combination with yellow fluorescent powder). Each of two blue LED dies, which emit the same light color, may be adopted in combination with a respective one of yellow fluorescent powders, which has a specific composition of compounds at a specific weight ratio, to constitute a white LED package light source that emits a substantially same white color. However, spectral characteristics of the white LED package light sources may be distinct from each other because of the different fluorescent powders used thereby. Therefore, even though the CIE coordinates may be utilized to analyze and define the light color emitted from the white LED package light source, the spectral characteristics of the white LED package light sources may not be obtained through the CIE coordinate analysis, and whether the white LED package light sources are constituted by the same combination of a LED die and fluorescent powder is unknown. In other words, it is insufficient to rely on CIE coordinates for analyzing and sorting different light sources.